Avoid SIGSEGV when heapster addon will be disabled

cmd/minikube/cmd/config/disable.go

@@ -33,6 +33,9 @@ var addonsDisableCmd = &cobra.Command{
 		}
 
 		addon := args[0]
+		if addon == "heapster" {
+			exit.WithCodeT(exit.Unavailable, "There is no heapster addon")
+		}
 		err := addons.SetAndSave(ClusterFlagValue(), addon, "false")
 		if err != nil {
 			exit.WithError("disable failed", err)